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Apparatus and method for maintaining cache/main memory consistency utilizing a dual port FIFO buffer

  • US 5,276,849 A
  • Filed: 07/07/1992
  • Issued: 01/04/1994
  • Est. Priority Date: 09/11/1989
  • Status: Expired due to Term
First Claim
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1. Apparatus coupled to a first agent that is coupled to a system bus, the apparatus temporarily storing data received from the first agent before the data is written to a system memory means that is also coupled to the system bus, comprising:

  • buffer storage means, said buffer storage means including,a first storage means for storing a unit of data having a predetermined number of bits, the first storage means having an output coupled to the system bus;

    a second storage means for storing a system memory means command for indicating a system memory means write operation for a unit of data stored within the first storage means, the system memory means command selectively specifying a full word memory means write operation or a partial word memory means write operation, the second storage means having an output;

    a third storage means for storing a system memory means address at which a stored unit of data is to be written in accordance with a system memory means command that is stored within the second storage means, the third storage means having an output coupled to the system bus;

    the apparatus further including,buffer means having an input coupled to said output of said second storage means and an output coupled to the system bus;

    detecting means, having an input coupled to the system bus and an output, for detecting from the system bus an occurrence of a write access by a second agent to the system memory means; and

    logic means, having an input coupled to the output of the detecting means and an output coupled to said buffer means, the logic means being responsive to the detecting means detecting an occurrence of a write access by the second agent to the system memory means and further being responsive to the first storage means having a unit of data stored therein, during an occurrence of the write access by the second agent, for causing the output of said buffer means to change from a first condition, wherein a full word write system memory means command is transmitted over the system bus to the system memory means without regard for the system memory means command that is stored within the second storage means, to a second condition wherein the system memory means command that is stored in the second storage means is transmitted through said buffer means to the system bus and to the system memory means.

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